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Gianfrancesco Villani, Lorenzo Bertelli, Giovanni Sato, Marco Morales, August Colenbrander; Central And Paracentral Single-Letter Recognition In Eyes With Macular Lesions. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5025. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the size, location, and number of single letters that can be recognized within 5° from fixation by patients with central vision loss
32 eyes (29 patients) with maculopathy (AMD, myopic maculopathy, macular edema, cone dystrophy, toxo scar) were enrolled. Lower-case single letters (TimesNewRoman) were randomly projected on a 19” LCD monitor at a viewing distance from 10 to 60 cm with black-on-white contrast polarity, >90% contrast, by custom software (“Letter Scotometry” [LS]). A two steps procedure was followed: 1- central size threshold (“CST”): central projection of a single letter at decreasing sizes from 0.63M to 25M in log steps until the answer was correct (≥3/5 letters per size); 2- paracentral span test (“PST”): random projection of single letters around a central small fixation dot into a grid of adjoining cells proportional to letter size. The letter size was set one log step bigger than CST, and not scaled by eccentricity (it could be increased if the patient read no letter, but then PST was restarted from the beginning). Stimuli stayed on screen until an answer was given, and the response-time was recorded. The only control of fixation was based on operator-patient interaction. The examination included ETDRS BCVA at 1m, MNREAD, SKREAD, and Microperimetry (MP) by Nidek MP1 or OPKO. Digital overlapping of letter-grids and microperimetry maps was done to compare scotoma borders in 8 directions from fixation and to understand if correct letters matched with the scotoma-free areas
BCVA median (range) was 0.75 (0.2-1.6) logMAR, CST was 0.84 (0.50-2.00) logMAR, MNREAD critical print size (CPS) was 0.9 (0.5-1.3) logMAR and SKREAD CPS was 0.9 (0.4-1.4) logMAR. Maximum Reading Speed (MRS) was 71.4 (2.4-162.2) wpm on MNREAD, and 25.5 (1.2-49.6) wpm on SKREAD. When the fixation dot was placed on the PRL the correspondence of scotoma borders between letter-grids and microperimetry was 74% (median 75%). CST on the LS test was strongly correlated with CPS (r 0.71) and minimum print size (r -0.77) on the SKREAD
LS grids can be used clinically to display fixation/PRL behavior in recognizing single-letters of the magnification needed for the low-vision patient to read in the presence of central scotomas
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